In the preparation of food products in separate cooking operations, various parameters are recognized as requiring relatively close tolerance to provide cooked products having appearance and taste characteristics within desired limits. In seeking after such product quality control, the industry has heretofore directed efforts to improvements in control of cooking medium temperature and to containment of the cooking medium to prevent contamination as in continuous-flow (recirculating) systems shown in U.S. Pat. No. 3,608,472 to Pelster et al. Further, the art has looked to on-line filtration of the cooking medium, i.e., during cooking operations.